The tau particle (so named because it was the third charged lepton, behind the electron and muon) was discovered in the 1970s by Martin Perl and colleagues. In one of the SLAC papers, Perl refers to the particle as the "$\tau$ lepton".
I've heard the particle referred to as the "tau", the "tau lepton", the "tau particle", and other variants substituting in "$\tau$" for "tau". I've also heard it referred to as the "tauon", in keeping with the muon and electron. I've only heard it used from a few sources, though. I have no idea where the term originally came from, though.
As an interesting side note, the Wikipedia talk page is in a furor over this. I have no idea if anyone on that page is actually who they say they are, or if any sources they give are true, but it seems that regardless of whether or not "tauon" is a valid term, nobody seems to know where it comes from.1
Where did the term "tauon" come from? Was it from Perl, or was it from someone completely different?
1 In theory, there have been worse disputes, but I find the "tau"/"tauon" one more amusing.